The present invention deals with the disciplines of medicinal chemistry, neurophysiology, and neuropharmacology. Specifically, the present invention is related to increasing levels of acetylcholine by the administration of 2-aryl-3-aroylbenzo[b]thiophenes.
Cholinergic neurons make up a major neuronal system of the central and peripheral nervous systems. Cholinergic neurons are associated especially with the neurotransmitter acetylcholine. In the central nervous system, acetylcholine is a neurotransmitter and can be found in, among other places, the hippocampus and frontal cortex of the brain.
The hippocampal area of the brain, particularly those areas which are known to involve cholinergic neurons, is believed to have functions associated with cognition, learning, and memory. Degenerative diseases with symptoms such as loss of cognition, learning, and memory, have been linked to a loss in cholinergic neurons. For example, it is known that in patients suffering from Alzheimer""s disease, there is a marked decrease in the level of cholinergic neurons in the hippocampus. The progressive loss of these cholinergic neurons appears to mirror the progressive loss in memory and cognitive function in these patients. It is thought that one reason for the decline of these neurons is the loss or decreased function of the neurotransmitter, acetylcholine. Several potential therapies which are designed to increase levels of acetylcholine are being clinically evaluated.
The level of acetylcholine in a neuron is basically determined by where the equilibrium between its biosynthesis and bio-degradation lies. The enzyme choline acetyltransferase (ChAT) is primarily responsible for its synthesis and acetylcholineesterase (AChE) for its degradation. One therapeutic strategy for increasing the level of acetylcholine is based on blocking its degradation via inhibition of AChE, e.g., using AChE inhibitors such as physostigmine salicylate, tacrine hydrochloride, donepezil hydrochloride and the like. Although, there are some encouraging results with the clinical use of AChE inhibitors, especially in early stages of Alzheimer""s disease, these agents generally have undesirable side effects, because of their non-specific, systemic action. Currently, tacrine has been approved for the early treatment of Alzheimer""s symptoms, (See xe2x80x9cGoodman and Gilman""s, The Pharmacological Basis of Therapeuticsxe2x80x9d, Ed. Gilman, et al., Pergamon Press, 8th Ed., Chap.7, (1990) and references cited, therein).
Another therapeutic strategy for increasing levels of acetylcholine is based on up-regulating ChAT in the neurons. It has been found that the hormone, estrogen, increases the level of acetylcholine by up-regulating ChAT in the hippocampus of rats (see xe2x80x9cImmunochemical demonstration of increased choline acetyltransferase concentration in rat preoptic area after estradiol administrationxe2x80x9d, Luine, et al., Brain Res., 191:273-277, 1980, xe2x80x9cEstradiol Increases Choline Acetyltransferase Activity in Specific Basal Forebrain Nuclei and Projection Areas of Female Ratsxe2x80x9d, Luine, V., Exp. Neurology, 89:484-490, 1985, xe2x80x9cOvarian steroid deprivation results in a reversible learning impairment and compromised cholinergic function in female Sprague-Dawley ratsxe2x80x9d, Singh, M., et al., Brain Res., 644:305-312, 1994). It, therefore, has been speculated, and preliminary clinical information confirms, that post-menopausal women treated with hormone replacement therapy (estrogen with or without progestins) may be less likely to succumb to Alzheimer""s disease or should have existing symptoms alleviated.
However, therapy with estrogen has undesirable side-effects, including uterotrophic effects, a possible increase in breast cancer incidence, bloating, resumption of menses, etc., which limits patient compliance. Thus, the opportunity exists for new and improved therapeutic interventions to increase levels of acetylcholine.
The current invention relates to a method for up-regulating choline acetyltransferase (ChAT) in mammals comprising administering to a mammal in need thereof, an effective amount of a compound of formula I: 
or a pharmaceutical acid addition salt or solvate thereof; where:
R1 and R3 are independently hydrogen, methyl, benzoyl, substituted benzoyl, or C(O)xe2x80x94(C1-C6 alkyl);
R2 is selected from the group pyrolidin-1-yl, piperidin-1-yl, and hexamethyleneimin-1-yl; where R2 is optionally the N-oxide; and optionally a choline esterase inhibitor.
In addition, the present invention relates to a method for increasing the levels of acetylcholine in the frontal cortex and/or hippocampus regions of the brain in mammals comprising administering to a mammal in need thereof, an effective amount of a compound of formula I, or a pharmaceutical acid addition salt or solvate thereof; and optionally a choline esterase inhibitor.
Further, the present invention relates to a method for inhibiting conditions or detrimental effects caused by a deficiency of choline acetyltransferase and/or acetylcholine in the frontal cortex and/or hippocampus regions of the brain in mammals comprising administering to a mammal in need thereof, an effective amount of a compound of formula I, or a pharmaceutical salt or solvate thereof; and optionally a choline esterase inhibitor.
Moreover, the present invention relates to a pharmaceutical formulation comprising a compound of formula I, or a pharmaceutical acid addition salt or solvate thereof, an acetylcholineesterase (AChE) inhibitor; and a pharmaceutical carrier, diluent, or excipient.
The current invention is related to the discovery that a select group of 2-aryl-3-aroylbenzo[b]thiophenes , i.e., compounds of formula I, are useful for up-regulating CHAT, and, therefore, are useful for increasing levels of acetylcholine in neurons which contain acetylcholine and ChAT.
A preferred embodiment of all methods of the present invention is where the mammal to be administered a compound of formula I is a human, particularly a female human, and most particularly when that human female is estrogen deficient. However, human males are also contemplated under the term xe2x80x9cmammalxe2x80x9d, particularly males who are testosterone deficient.
Another preferred embodiment of the present invention is where the condition caused by a decrease of choline acetyltransferase and/or acetylcholine in the frontal cortex and/or hippocampus regions of the brain is Alzheimer""s disease.
Moreover, another preferred embodiment of all methods of the present invention is the use of a pharmaceutical acid addition salt of a compound of formula I where R1 and R3 are hydrogen and R2 is pyrolidin-1-yl. More preferably, the salt is the hydrochloride. This more preferred compound is named [2-(4-hydroxyphenyl)-6-hydroxybenzo[b]thien-3-yl][4-[2-(1-pyrolidinyl)ethoxy]phenyl]methanone hydrochloride.
An even more preferred embodiment of all methods of the present invention is the use of a pharmaceutical acid addition salt of a compound of formula I where R1 and R3 are hydrogen and R2 is piperidin-1-yl. Most preferably, the salt is the hydrochloride. This most preferred compound is named [2-(4-hydroxyphenyl)-6-hydroxybenzo[b]thien-3-yl][4-[2-(1-piperidinyl)ethoxy]phenyl]methanone hydrochloride or raloxifene hydrochloride.
The present invention contemplates the optional use of currently known AChE inhibitors such as physostigmine salicylate, tacrine hydrochloride, donepezil hydrochloride and the like, as well as agents that are later found to be AChE inhibitors.
As used herein, the term xe2x80x9ceffective amountxe2x80x9d means an amount of a compound of formula I which is capable of up-regulating CHAT and/or increasing levels of acetylcholine in the hippocampus and frontal cortex regions of the brain and/or inhibiting conditions or detrimental effects caused by a decrease of choline acetyltransferase and/or acetyl in mammals. When a compound of formula I is co-administered with an AChE inhibitor the term xe2x80x9ceffective amountxe2x80x9d also means an amount of such an agent capable of inhibiting AChE.
The term xe2x80x9cestrogen deficientxe2x80x9d refers to a condition, either naturally occurring or clinically induced, where a woman can not produce sufficient estrogenic hormones to maintain estrogen dependent functions, e.g., menses, homeostasis of bone mass, neuronal function, cardiovascular condition, etc. Such estrogen deprived situations arise from, but are not limited to, menopause and surgical or chemical ovarectomy, including its functional equivalent, e.g., medication with GnRH agonists or antagonists, ICI 182780, and the like.
The term xe2x80x9cinhibitingxe2x80x9d in the context of inhibiting conditions or detrimental effects caused by a deficiency of ChAT and/or acetylcholine in the frontal cortex and/or hippocampus regions of the brain includes its generally accepted meaning, i.e., prohibiting, restraining, alleviating, ameliorating, slowing, stopping, or reversing the progression or severity of a decrease in ChAT and acetylcholine and the pathological sequelae, i.e., symptoms, resulting from that event.
The term xe2x80x9cup-regulating ChATxe2x80x9d refers to increasing the enzymatic activity of ChAT, i.e., promoting the conversion of choline to acetylcholine. This promotion would include an increase in the efficiency and/or rate of reaction of CHAT and choline and/or an increase in the amount of CHAT present at the site of action. This increase in the amount of enzyme present may be due to gene regulation or other synthetic step of the enzyme""s formation and/or a decrease in the enzyme""s de-activation and metabolism.
General terms used in the description of compounds herein described bear their usual meanings. For example, xe2x80x9cC1-C6 alkylxe2x80x9d refers to straight, branched, or cyclic aliphatic chains of 1 to 6 carbon atoms including methyl, ethyl, propyl, iso-propyl, cyclopropyl, n-butyl, pentyl, hexyl and the like.
The term xe2x80x9csubstituted benzoylxe2x80x9d refers to benzoyl group having one to five substituents selected independently from the group C1-C4 alkyl, C1-C4 alkoxy, hydroxy, nitro, chloro, fluoro, or tri(chloro or fluoro)methyl.
The term xe2x80x9cpharmaceuticalxe2x80x9d when used herein as an adjective, means substantially non-toxic and substantially non-deleterious to the recipient.
By xe2x80x9cpharmaceutical formulationxe2x80x9d it is further meant that the carrier, solvent, excipients and salt must be compatible with the active ingredient of the formulation (a compound of formula I).
The term xe2x80x9cacid addition saltxe2x80x9d refers to a salt of a compound of formula I prepared by reaction of a compound of formula I with a mineral or organic acid. For exemplification of pharmaceutical acid addition salts see, e.g., Berge, S. M, Bighley, L. D., and Monkhouse, D. C., J. Pharm. Sci., 66:1, 1977.
The term xe2x80x9csolvatexe2x80x9d represents an aggregate that comprises one or more molecules of the solute, such as a formula I compound, with one or more molecules of a pharmaceutical solvent, such as water, ethanol, and the like.
Compounds of formula I where R and/or R3 are hydrogen or methyl may be prepared according to known procedures, such as those detailed in U.S. Pat. Nos. 4,133,814, 4,418,068, and 5,731,342, the teachings of each are herein incorporated by reference. The compounds of formula I which are carboxylic esters (R1 and/or R3 are C(O)xe2x80x94(C1-C6 alkyl), benzoyl, or substituted benzoyl) may be prepared from compounds of formula I where R and/or R3 are hydrogen by methods described in U.S. Pat. No. 5,393,763, the teachings of which are herein incorporated by reference.
The pharmaceutical acid addition salts of the invention are typically formed by reacting a compound of formula I with an equimolar or excess amount of acid. The reactants are generally combined in a mutual solvent such as diethylether, tetrahydrofuran, methanol, ethanol, isopropanol, benzene, and the like. The salts normally precipitate out of solution within about one hour to about ten days and can be isolated by filtration or other conventional methods.
Acids commonly employed to form acid addition salts are inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, phosphoric acid, and the like, and organic acids such as p-toluenesulfonic, methanesulfonic acid, ethanesulfonic acid, oxalic acid, p-bromophenylsulfonic acid, carbonic acid, succinic acid, citric acid, tartaric acid, benzoic acid, acetic acid, and the like.
Physostigmine salicylate, tacrine hydrochloride, donepezil hydrochloride and other AChE inhibitors are commercially available.
Pharmaceutical formulations can be prepared by procedures known in the art, such as, for example, in EP Published Application 670162A1, published Sep. 6, 1995, and in WO 97/35571 published Oct. 2, 1997, both of which are herein incorporated by reference. For example, a compound of formula I, and optionally an AChE inhibitor, can be formulated with common excipients, diluents, or carriers, and formed into tablets, capsules, and the like. Thus, a compound of formula I and an AChE inhibitor can be formulated and administered together. A compound of formula I and an AChE inhibitor may also be administered separately.
Examples of excipients, diluents, and carriers that are suitable for formulation include the following fillers and extenders such as starch, sugars, mannitol, and silicic derivatives; binding agents such as carboxymethyl cellulose and other cellulose derivatives, alginates, gelatin, and polyvinyl pyrrolidone; moisturizing agents such as glycerol; disintegrating agents such as agar, calcium carbonate, and sodium bicarbonate; agents for retarding dissolution such as paraffin; resorption accelerators such as quaternary ammonium compounds; surface active agents such as cetyl alcohol, glycerol monostearate; adsorptive carriers such as kaolin and bentonire; and lubricants such as talc, calcium and magnesium stearate and solid polyethyl glycols. Final pharmaceutical forms may be pills, tablets, powders, lozenges, syrups, aerosols, saches, cachets, elixirs, suspensions, emulsions, ointments, suppositories, sterile injectable solutions, or sterile packaged powders, depending on the type of excipient used.
Additionally, the compounds of formula I are well suited to formulation as sustained release dosage forms. The formulations can also be so constituted that they release the active ingredient only or preferably in a particular part of the intestinal tract, possibly over a period of time. Such formulations would involve coatings, envelopes, or protective matrices which may be made from polymeric substances or waxes.
The particular dosage of a compound of formula I required to up-regulate ChAT, and optionally the dosage of an AChE inhibitor required to inhibit AChE, according to this invention will depend upon the particular circumstances of the conditions to be treated. Considerations such as dosage, route of administration, and frequency of dosing are best decided by the attending physician. Generally, an effective minimum dose for oral or parenteral administration of a compound of formula I is about 1, 5, 10, 15, or 20 mg. Typically, an effective maximum dose is about 800, 100, 60, 50, or 40 mg. A particularly effective amount is 60 mg of raloxifene hydrochloride (56 mg of free base) per day via an oral route of administration. Such dosages will be administered to a patient in need of treatment from one to three times each day or as often as needed to effectively up-regulate ChAT, and/or increase the levels of acetylcholine in the frontal cortex and/or hippocampus regions of the brain and/or inhibit conditions or detrimental effects caused by a deficiency of choline acetyltransferase and/or acetylcholine in the frontal cortex and/or hippocampus regions of the brain.